High intensity lamp containing internal shorting fuse

ABSTRACT

A high intensity lamp comprising an arc tube containing metal vapor such as sodium and mercury mounted within an evacuated outer jacket based at one end. The possibility exists of a destructive power arc forming within the vacuum jacket should there occur a leak of air into the jacket or should the arc tube fail resulting in a partial pressure of gas in the outer bulb. A self-shorting arcing fuse is provided within the jacket to extinguish such arc safely and end the life of the lamp. A second self-shorting arcing fuse may also be built into the base as an additional safety measure.

United States Fatent Collins et al.

[ Oct. 23, 1973 HIGH INTENSITY LAMP CONTAINING INTERNAL SHORTING FUSE [75] Inventors: Byron R. Collins, Euclid; Juris Sulcs, Cleveland; Charles I. McVey, Shaker Heights, all of Ohio [73] Assignee: General Electric Company,

Schenectady, N.Y.

[22] Filed: Mar. 1, 1972 [21] Appl. No.2 230,761

[52] US. Cl. 315/75, 315/125 [51] Int. Cl. IIOIj 61/04 [58] Field of Search 315/74, 75, 125

[56] References Cited UNITED STATES PATENTS 3,222,556 12/l965 Gustin 315/91 X Primary Examiner-Roy Lake Assistant Examiner.lames B. Mullins Attorney-Ernest W. Legree et al.

[57] ABSTRACT A high intensity lamp comprising an arc tube containing metal vapor such as sodium and mercury mounted within an evacuated outer jacket based at one end. The possibility exists of a destructive power are forming within the vacuum jacket should there occur a leak of air into the jacket or should the arc tube fail resulting in a partial pressure of gas in the outer bulb. A self-shorting arcing fuse is provided within the jacket to extinguish such are safely and end the life of the lamp. A second self-shorting arcing fuse may also be built into the base as an additional safety measure.

HIGH INTENSITY LAMP CONTAINING INTERNAL SHORTING FUSE BACKGROUND OF THE INVENTION The invention relates to high intensity vapor arc lamps comprising an inner envelope mounted within a vacuum outer envelope. It is particularly usefulwith the larger sizes of high intensity sodium vapor lamps of the kind described in US. Pat. No. 3,248,590 Schmidt, entitled High Pressure Sodium Vapor Lamp.

Such lamps utilize an elongated inner envelope of ceramic material such as a high density polycrystalline alumina tube which is resistant to sodium at high temperatures to contain the arc. The filling comprises an amalgam of sodium and mercury and a rare gas, preferably xenon, to facilitate starting. Each end of the alumina tube is sealed by a refractory metal closure member, suitably a niobium end cap which serves as an electrical inlead and supports an electrode internally. The ceramic arc tube is supported within an outer vitreous envelope or jacket having at one end a screw base providing terminals to which the end caps of the arc tube are connected. The jacket is evacuated in order to conserve heat and maintain the cold spot or lowest temperature portion of the arc tube at a sufficiently high temperature.

The high pressure sodium vapor lamp has a relatively high starting voltage due in part to the small diameter of the arc tube and the use of xenon as a starting gas. Also the metal end cap used for the arc tube closures does not lend itself conveniently to the incorporation of an auxiliary starting electrode. To start and operate the lamp, a ballast circuit is generally used which supplies a high voltage pulse, customarily near the peak of the open circuit waveform, until the lamp ignites. The pulsing circuit is disabled by the reduction in voltage at the lamp terminals from the open circuit value to the lamp running value, and the pulse is discontinued until the next time the lamp is started. When the lamp fails, the ballast continues to supply high voltage pulses until power is disconnected or the lamp is replaced. The lamp socket and the fixture wiring must have insulation capable of withstanding the highvoltage pulses from the ballast over extended periods of time.

SUMMARY OF THE INVENTION sodium vapor lamps particularly in the larger sizes such as lamps of 700 watts and 1,000 watts rating or higher is the possibility of a destructive failure resulting from uncontrolled arcing. Since the outer jacket has been evacuated to a high vacuum, it does not appear possible that a power are could develop within it. After destructive arcing there is little of the lamp-left to examine and the occurrence would readily be attributed to some unnoticed internal defect within the lamp. However we have found that perfectly good lamps may develop faults during life which will lead to destructive arcing. We have determined and confirmed experimentally that there are two situations which may occur in which a destructive power are will start in the jacket. The first situation is that wherein the vacuum outer jacket develops a slow air leak, for instance as a result of mishandling or heat shock. As the internal pressure rises from a condition of high vacuum to -20 torr, the breakdown voltage across the stem leads within the jacket will drop to a few hundred volts. In the case of the 1,000 watt lamp, the ballast has an open circuit voltage of approximately 480 volts which may be adequate to initiate a glow discharge, and the high voltage pulses supplied by the ballast circuit will in any event assure ignition of a discharge. As the discharge is prolonged, the metal parts become heated up, and with increasing pressure, the glow discharge changes over into a destructive power arc. This are is usually stable from a pressure of a few torr to full atmospheric pressure and hence will not be extinguished as the bulb airs up further. The high power in the arc may cause the relatively heavy hard glass outer jacket to fall off and this constitutes a hazard. Also the arc may continue into the base and socket and damage the fixture or destroy the wir- The second situation under which a power are may form within the jacket occurs when the arc tube develops a leak. The release of sodium and mercury vapor and the arc tube starting gas into the jacket may cause an arc to start between the metal parts about the stem. Even though the sodium and mercury vapor rapidly condense on the relatively cool jacket walls and their residual pressure in the much larger volume of the outer jacket would not support an arc, the are once started can maintain itself in the vapor of the metal I parts such as iron or nickel inleads and supports to which it attaches. Hence the arc will not be extinguished and can continue to the ultimate destruction of the lamp and its socket and wiring.

In accordance with our invention, we forestall the possibility of a destructive power are by providing a self-shorting arcing fuse within the jacket to extinguish any such arc and safely end the life of the lamp without damage to the socket or wiring. This mode of arc extinction is particularly suitable where a short circuited mode of operation has been provided for in the design of the auxiliary equipment or ballast. The fuse is located within the jacket and preferably close to the stem where the inleads emerge into the jacket or interenvelope space. The fuse structure defines the closest spatial approach between opposite current conductors within the jacket, or in other words the minimum gap between the inleads. Thus, should a glow discharge start within the jacket, when transition from glow to arc discharge takes place, the arc will ultimately occur across the shortest gap which is that defined by the fuse. The metal conductors of the fuse are interlinked and so arranged that heat deformation or collapse upon continuance of the power arc will cause one conductor to bridge over to the other and short circuit the gap. In one fusing arrangement a metallic loop portion of one conductor encircles a portion of the opposite conductor in close proximity. The loop is of a metal that will soften and flow without excessive oxidation, for instance nickel or iron, and upon fusing together will cause a direct short which extinguishes the arc. The loop or interlocking arrangement assures that the fusing system will work in any orientation of the lamp.

In a preferred construction, a self-shorting arcing fuse is also built into the base in order to extinguish any are which may form therein,for instance as a result of faulty wiring or accumulated soil or excessive humidity and condensation.

In the drawings:

FIG. 1 is a front view of a high pressure sodium vapor lamp embodying the invention with the front portion of the outer jacket and base cut away to expose the internal construction.

FIG. 2 is a sectional view through the lamp taken at plane 2-2 and looking towards the base and in the direction indicated by the arrows.

FIG. 3 is a view of the neck end of the lamp showing the fuse arced over and shorted.

FIG. 4 is a view of the neck end of a similar lamp showing an alternative fuse construction which is a variant of the invention.

DETAILED DESCRIPTION Referring to the drawing and more particularly to lamp I comprising an outer tubular vitreous envelope or jacket 2. A central portion of the lamp has been omitted to facilitate illustration. The jacket is made of a high temperature glass such as borosilicate glass and is relatively thick-walled in order to withstand atmospheric pressure. The neck 3 of the jacket is closed by a re-entrant stem 4 terminated in a press 5 through which extend heavy inleads or current conductors 6,7 which are connected respectively to the threaded shell 8 and insulated center contact 9 of a conventional screw base. The base is mechanically retained on the neck of the jacket by screwing shell 8 over threaded retaining ring 10 which has inwardly turned notches 11 which engage corresponding dimples in the glass of the neck.

The inner envelope or are tube 15 is made of sintered high density polycrystalline alumina ceramic per U.S. Pat. No. 3,026,210 Coble, Transparent Alumina and Method of Preparation, or of other lighttransmitting ceramic capable of withstanding the attack of sodium vapor at high temperatures. The tube is closed by thimble-like niobium metal end caps 16, 17 having skirt portions which fit around the ends of the tube. The end caps are sealed to the alumina by means of a sealing composition comprising a major proportion of aluminum oxide and calcium oxide and a minor proportion of magnesium oxide and barium oxide.

Thermionic electrodes are mounted in the ends of the arc tube and supported from the end caps. Lower electrode 19 is shown in the drawing and comprises a tungsten wire coil or helix 20 wound around a tungsten shank or core 21 fastened in the end of a niobium tube 22 welded through the end cap. The electrodes are activated by metal oxides retained in the interstices between turns of the coil, a preferred material being dibarium calcium tungstate Ba- CaWO as described and claimed in copending application Ser. No. 97,907 filed Dec. 14, 1970 by William E. Smyser et al., entitled Discharge Lamp Thermionic Cathode Containing Emission Material," and assigned to the same assignee as this invention, now U.S. Pat. No. 3,708,800. Lower niobium tube 22 has an opening into the ceramic arc tube which serves as an exhaust port during manufacture. The ionizable filling consisting of an inert gas, preferably xenon at a cold filling pressure of about 20 torr, and a sodium-mercury amalgam is introduced through exhaust tube 22 which is then hermetically pinched off by a cold weld indicated at 24. Upper niobium tube 23 has no opening into the arc tube and may be used to contain a small quantity of yttrium metal serving as a getter. In operation of the lamp, lower tube 22 is the coolest portion of the arc tube and serves as a reservoir for excess sodium-mercury amalgam. The illustrated lamp is intended for base-up operation; in a base-down version of the same lamp, the arc tube is reversed relative to the outer jacket and longer exhaust tube 22 is located at the base end so that it is again lowermost in operation.

The are tube is supported within the jacket by a mounted comprising a side rod 26 made of two wires spot-welded together for greater stiffness, welded to inlead 6 close by the press and extending the length of the envelope. Leaf spring members 27 at the stem end and 28,29 at the dome end bear against the tubular jacket to maintain rod 26 in place. Alumina ceramic has a substantial coefficient of expansion and the range of temperature traversed by the arc tube exceeds l,000 C. To allow for expansion, only the lower exhaust tube 22 is completely restrained, being welded between straps 31 bridged across laterally extending portion 32 of the side rod. The upper tube 23 extends freely through an encircling opening formed between straps 33 extending from side rod 26 to short support rod 34 which is welded to inlead 7 and braced by leaf spring 35. Ceramic sleeve 36 electrically insulates straps 33 from side rod 26. The electrical connection to end cap 16 of the arc tube is provided by flexible strap 37 welded thereto. The space within outer jacket 3 is evacuated to a high vacuum in order to reduce heat loss from the arc tube. Air is pumped out through exhaust tube 38 prior to tip-off and barium-containing getter rings 39 are then flashed to assure a high vacuum.

In accordance with our invention we provide a self shorting arcing fuse within the jacket and close by the stern where the inleads 6,7 emerge into the jacket or interenvelope space. As shown in FIGS. 1 and 2, a short length of solid wire 41 is welded to inlead 7 close below press 5 and extends towards inlead 6 where it terminates in a loop or ring 42 which closely encircles inlead 6 but is spaced therefrom. Inlead 6 and ring 42 define the closest approach between opposite current conductors within the jacket, that is they define the minimum gap between any conductors connected to inleads 6 and 7. This insures that should a glow discharge start within the jacket, when transition from glow to are discharge takes place, the arc will occur about loop 42. Wire 41 and inlead 6 are made of metal that will soften and flow without excessive oxidation, preferably of nickel or alternatively of iron. These materials have relatively high surface tension when molten so that the ends tend to ball up and grow in size, facilitating the bridging action which eventually short-circuits the gap. When loop 42 fuses to inlead 6, it forms a direct short circuit which extinguishes the arc. The fact that loop 42 encircles inlead 6 assures that the softened metal will flow and fuse together regardless of the orientation of the lamp, as shown at 43 in FIG. 3.

In a design of the lamp suitable for factory production, we prefer to place a short glass sleeve 44 around inlead 6 immediately below the press 5. Wire 41 is welded to inlead 6 and loop 42 in its end snugly encircles glass sleeve 44. The presence of glass sleeve 44 assures proper spacing of the loop 42 around inlead 6 and avoids the need for critical adjustment and spacing of parts by the assembler. At the same time, sleeve 44 is short enough that should a discharge occur within the jacket, the arc will jump across the shortest gap which is from loop 42 to inlead 6 around one end or the other of the sleeve. Th sleeve is made of a high lead content glass which melts at relatively low temperature, for. instance a glass containing or more lead oxide by weight. The use of lead glass for sleeve 44 assures a low resistance joint when the metal parts fuse together and is desirable for reliable operation. We have found it desirable to provide also a glass sleeve 45 around the portion of wire 41 that extends between inleads 6 and-7 to forestall any tendency of the arc to form on that portion of the wire. The composition of the glass sleeve 45 is not important and can be for example borosilicate, lime, or lead glass or any other suitable dielectric.

We have found it desirable to provide a second selfshorting arcing fuse in the base of the lamp in order to extinguish any arc which might form therein. The high open circuit voltage, and particularly the high voltage pulses utilized to start the lamp, may cause an arc to form within the base should the internal wiring be faulty or should there be accumulated soil or excessive humidity and condensation within the base. An example of faulty wiring might be the case where insufficient separation is maintained between the inleads as they are directed one to the end contact, and the other to the base shell. The outer arcing fuse may be similar to that described and claimed in US. Pat. No. 2,950,417-Breeding' et al, Series Electric Lamp, August 1960, and is located within the stem tube of the jacket and enclosed within base shell 8 so that it is in outside air. lnleads 6,7 have solid wire inner portions of nickel within the outer jacket, tungsten portions where they pass through the press 5, and external portions 6a,7a of flexible stranded nickel plated copper wire wrapped around a solid nickel core wire. Lead wire portion 7a is passed through a slender thin-walled glass sleeve 46 extending through stem tube 4 alongside jacket exhaust tube 38 and its end as welded to end contact 9. Lead wire portion 6a is wrapped one or more turnsaround glass sleeve 46 and exhaust tube 38 to gether, and its end is welded to retaining ring 10 which is engaged by shell 8 of the base.

Should an arc develop in thebase of the lamp, it will seek the closest approach of stranded lead-in wire portions 6a,7a to each other. Glass sleeve 46 is made of high lead content glass which becomes relatively conductive when heated. Upon being touched by the arc, sleeve 44 will melt and permit a conductive juncture to be formed between wires 6a,7a which will short circuit the arc.

An alternative self-shorting fuse construction is I shown in FIG. 4. Interengaging loops 47,48 of solid wire are welded to inleads 6 and 7 close below press 5. One loop leans in a direction opposite to the other and one passes through the other like half links in a chain. The loops are spaced to define the minimum gap within the jacket between any conductor connected to inleads 6 and 7. They are made of metal, for instance nickel, that will soften and flow without excessive oxidation upon occurrence of an arc, whereby to form a short circuit that extinguishes the arc. The interengagement of the loops assures successful operation for any orientation of the lamp. The fuse construction in the jacket shown in FIG; 4 may be combined with a self-shorting fuse within the base as previously described with reference to FIG. 1.

By means of an internal self-shorting fuse within the jacket the invention overcomes the hazards which we have found to exist in high starting voltage metal vapor lamps utilizing vacuum outer jackets.

The fuse constructions described have been tested and found reliable but modifications or variants thereof performing the same functions may of course be utilized.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A vacuum jacketed high intensity vapor arc lamp comprising:

an evacuated vitreous outer envelope having inleads sealed therein; an inner elongated envelope containing ionizable vapor and having electrodes sealed into its ends;

said inner envelope requiring a starting voltage high enough to start a discharge in said outer envelope should the vacuum therein be destroyed;

means supporting said inner envelope within said outer envelope and including conductors connecting said electrodes to said inleads; and

a short-circuiting arcing fuse in said outer envelope comprising metal conductors connected to said inleads and defining, at the closest spatial approach between opposite current conductors, a gap across which an are forming in said outer envelope will occur, said conductors being interlinked in such fashion that heat deformation thereof by an arc will cause one conductor to bridge over to the other about said gap for any orientation of said lamp.

2. A lamp as in claim 1 wherein each of the metal conductors defining said gap makes a part loop around the other but spaced one from the other the distance of said gap, said conductors being of metal that will soften and flow under heat without excessive oxidation.

3. A lamp as in claim 2 wherein said metal conductors making said loops are of nickel.

4. A vacuum jacketed high intensity metal vapor lamp comprising:

an evacuated vitreous outer envelope having a pair of stiff inleads sealed, therein at the neck end side by side through a press;

an inner elongated arc tube containing metal vapor and having electrodes sealed into its ends;

said are tube requiring a starting voltage high enough to start a discharge in said outer envelope should thevacuum therein be destroyed; means supporting said arc'tube within said outer envelope and including conductors connecting said electrodes to said inleads; and a short-circuiting arcing fuse in said outer envelope comprising a metal conductor connected to one inlead close to the press and extended into a loop which encircles the other inlead, said loop defining a gap which is the closest spatial approach between opposite current conductors so that any are forming will occur at said gap, said metal conductor being of metal that will soften and flow under heat without excessive oxidation whereby to bridge over said gap upon occurrence of an arc thereat.

5. A lamp as in claim 4 wherein said metal conductor is of metal selected from the group consisting of iron, nickel and alloys thereof.

6. A lamp as in claim 4 including a short sleeve of low melting point lead glass placed around said other inlead and encircled by said loop.

7. A lamp as in claim 4 including a base attached to the neck end of said envelope to which said inleads are connected, and an additional self-shorting arcing fuse located in said base.

8. A lamp as in claim 4 wherein the metal vapor includes sodium.

9. A lamp as in claim 4 wherein the arc tube contains I sodium, mercury and xenon.

* III l 

1. A vacuum jacketed high intensity vapor arc lamp comprising: an evacuated vitreous outer envelope having inleads sealed therein; an inner elongated envelope containing ionizable vapor and having electrodes sealed into its ends; said inner envelope requiring a starting voltage high enough to start a discharge in said outer envelope should the vacuum therein be destroyed; means supporting said inner envelope within said outer envelope and including conductors connecting said electrodes to said inleads; and a short-circuiting arcing fuse in said outer envelope comprising metal conductors connected to said inleads and defining, at the closest spatial approach between opposite current conductors, a gap across which an arc forming in said outer envelope will occur, said conductors being interlinked in such fashion that heat deformation thereof by an arc will cause one conductor to bridge over to the other about said gap for any orientation of said lamp.
 2. A lamp as in claim 1 wherein each of the metal conductors defining said gap makes a part loop around the other but spaced one from the other the distance of said gap, saId conductors being of metal that will soften and flow under heat without excessive oxidation.
 3. A lamp as in claim 2 wherein said metal conductors making said loops are of nickel.
 4. A vacuum jacketed high intensity metal vapor lamp comprising: an evacuated vitreous outer envelope having a pair of stiff inleads sealed therein at the neck end side by side through a press; an inner elongated arc tube containing metal vapor and having electrodes sealed into its ends; said arc tube requiring a starting voltage high enough to start a discharge in said outer envelope should the vacuum therein be destroyed; means supporting said arc tube within said outer envelope and including conductors connecting said electrodes to said inleads; and a short-circuiting arcing fuse in said outer envelope comprising a metal conductor connected to one inlead close to the press and extended into a loop which encircles the other inlead, said loop defining a gap which is the closest spatial approach between opposite current conductors so that any arc forming will occur at said gap, said metal conductor being of metal that will soften and flow under heat without excessive oxidation whereby to bridge over said gap upon occurrence of an arc thereat.
 5. A lamp as in claim 4 wherein said metal conductor is of metal selected from the group consisting of iron, nickel and alloys thereof.
 6. A lamp as in claim 4 including a short sleeve of low melting point lead glass placed around said other inlead and encircled by said loop.
 7. A lamp as in claim 4 including a base attached to the neck end of said envelope to which said inleads are connected, and an additional self-shorting arcing fuse located in said base.
 8. A lamp as in claim 4 wherein the metal vapor includes sodium.
 9. A lamp as in claim 4 wherein the arc tube contains sodium, mercury and xenon. 